Plastic Foams for Concrete HomesPortland Cement Association Residential Technology Brief

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All types of rigid foam insulation deliver solid performance when used in ICFs for residential construction. Each foam material exhibits unique performance properties dependent on the material density, dimensions, and other factors. With minor changes in the manufacturing process, different results—using the same type of plastic—can be achieved to meet exacting specifications. The minimum performance properties for rigid foam plastics and cement-foam composites serve as guidelines when selecting materials for an ICF system.

EPS offers exceptional value, providing ample insulation and resistance to air and moisture infiltration. At lower densities, it provides moderate strength. It also is available in either custom molded components or sheet form. EPS can be engineered to deliver higher R-value per inch and greater strength by increasing the material density. XPS is typically more expensive (up to 50%) and may offer a higher insulating value per inch. It exhibits higher strength properties and a slightly greater resistance to water absorption. It is available in sheet form only.

Polyurethane has a higher insulating value than either EPS or XPS and comparable strength, but is the most expensive rigid foam plastic. It is available in some molded ICF systems. A closely related foam, polyisocyanurate, is available in sheet form, but is not usually recommended for use in ICFs. Due to the use of cement, composite foam provides exceptional strength and possibly more durability with slightly lower insulating values. This type of ICF system is heavier than its rigid foam counterpart and typically requires more effort to cut and shape. Cost estimates are unavailable since the material is only available in completed, molded units.

Rigid foam plastics are considered to be inert materials with no recognized health effects. Polystyrene and polyurethane are formaldehyde-free and have not been linked to respiratory problems or skin irritations, as have some fiber-based insulations. In tests for indoor air quality, no harmful emissions were detected in wall systems using expanded polystyrene foams. All foams manufactured for use as insulation or other building applications incorporate a fire retardant intended to minimize flame spread in the event of a fire. Research on the fire performance of EPS rigid foam plastic concludes that when it is forced to burn in a simulated fire test, emissions are no more toxic than those of burning wood.

When comparing the effectiveness of one ICF system to another, a basic understanding of the different foam materials can prove helpful. However, it is most important to choose the best ICF system for your specific needs, not a particular type of foam. The performance of an ICF is only partly determined by the choice of foam used. ICF systems offer an integrated and unique approach to residential building and should be evaluated in terms of their overall performance, not individual components, to fully appreciate their benefits.

Rigid foam plastic insulation is an important feature of ICFs that contributes to a superior house. There is no one “best” material, but foams offer performance variables that can help explain the differences between ICF products.

For more information, visit www.concretehomes.com,www.epscentral.org, or www.forms.org. The following publications, available from PCA, also may be useful: